1. Field of the Invention
This invention relates to the field of communication receivers, and more particularly to a selective call communication receiver providing high speed data and voice communication with battery saving capability.
2. Description of the Prior Art
There are many communication systems in operation today, including virtually all of today's paging systems, which utilize frequency (FM) modulation for addressing, and for data and voice transmission. The current communication receivers, including paging receivers, utilize sophisticated receiver architectures, and today's paging systems utilize well known and established signaling formats. The current receiver architectures and signaling formats have been optimized to provide both high receiver sensitivities and excellent battery saving capabilities.
In many metropolitan areas, many paging systems were being operated at, or near, the maximum system capacity, in both the number of subscribers that can be accommodated, and the message transmission time that was available. Such paging system operation has resulted in reduced customer satisfaction due to extended holding, or "camp-on" times required to access the paging system, and also due to extended delays in message delivery due to equally extended paging system message transmission queues. In an effort to improve the message throughput in such prior art systems, such services as voice paging, were eliminated on many systems, and were replaced by newer services, such as numeric and alphanumeric messaging. These newer services greatly increased the number of subscribers which could be accommodated on the paging system, by greatly reducing the air-time requirements for message transmission. However, as the demand for even more improved paging services has increased, such as for improved methods for handling and processing large alphanumeric data messages, many paging systems are again nearing the maximum system capacity. In an effort to continue to improve the grade of service being provided in such paging systems, new signaling formats, such as the 1200 baud POCSAG signaling format, have been implemented to ease the burden on the paging system by providing ever increasing message throughput.
When used in simulcast transmission systems, standard FM modulation is not suitable for data transmission at high bit rates due to transmitter equalization problems. Because of the limitations of FM modulation for high speed message transmission, other forms of modulation, such as linear modulation techniques are required to provide for transmission at the higher data rates. While linear modulation techniques are available to provide the increased message transmission speeds, such modulation techniques generally are incompatible for use with existing receiver architectures, are incompatible with present day signaling protocols, and require significantly more current drain for operation than required for circuits receiving and demodulating existing signaling protocols transmitted using standard FM modulation techniques. There is a need to provide a receiver architecture which retains compatibility within existing FM modulated paging signaling protocols, thereby taking advantage of the battery saving capabilities of these existing paging signaling protocols. Furthermore, there is a need to provide a receiver architecture which includes linear demodulation for voice and high speed data capability, to provide the increased message throughput required for these ever expanding services, without compromising the battery saving performance of the existing paging signaling protocols.